Synthesis And Electrocatalytic Performance Of MOF-derived N-doped Porous Carbon Supported Platinum Catalysts

Direct methanol fuel cell（DMFC）has been widely used in automobile and portable electronic equipment due to its advantages of low energy consumption,simple system and high energy density.However,the anodic oxidation of methanol must overcome a polarization potential to achieve a high reaction rate,so the electrochemical performance of methanol oxidation is poor.At present,the common anodic catalyst for DMFC is Pt based catalyst.However,due to its lack of resources and high cost,and its vulnerability to the toxicity of intermediate products such as CO,it reduces the electrocatalytic activity and stability of methanol oxidation,which restricts the practical application of DMFC.Therefore,the development of Pt based catalysts with high electrochemical activity and stability is the focus of current DMFC research.The support has an important influence on the electrochemical performance of the catalyst,and the transport channels of electrons and substances are very important.Therefore,the pore structure of the support has an important influence on the stability and activity of the catalyst.Metal organic framework（MOF）has the unique properties of high specific surface area and crystal structure diversity,which provides a new idea for the design and synthesis of catalyst support.In this paper,nitrogen-rich MOF was used as the precursor to prepare nitrogen-doped porous carbon materials.Zeolite-like imidazole skeleton structure ZIF-67 is the precursor and melamine is the external nitrogen source,a novel Co embedded into nitrogen-doped carbon nanotube modified mesoporous carbon（Co@NCNTs-MC）material was synthesized by high temperature calcination.Together as the precursor,ZIF-67 and ZIF-8 were calcined at high temperature to form nitrogen-doped carbon nanotubes hollow porous carbon supports.A polypyrrole with high conductivity prepared by electrochemical oxidation polymerization was introduced to make ZIF-67 grow on the polypyrrole network for high temperature calcination and synthesis of nitrogen-doped porous carbon materials.Porous carbon materials for the above strategies preparation as a Pt based composite catalyst support,effectively improve the dispersion of Pt nanoparticles,at the same time,the existence of the porous carbon can enhance electronics material transport capacity,the electrocatalytic activity,stability and CO poisoning resistance of methanol oxidation were improved.The main contents of this paper are as follows:（1）A novel cobalt embedded into nitrogen-doped carbon nanotube-modified mesoporous carbon（Co@NCNTs-MC）carrier derived from metal organic framework（MOF）was synthesized by high temperature calcination method at the appropriate temperature and time using ZIF-67 as the precursor and melamine as the secondary nitrogen source.The presence of melamine ensured sufficient nitrogen content at high temperature,and Co nanoparticles promoted the formation of NCNTs in the pyrolysis process and formed mesoporous carbon structure,synthesized Pt composite catalyst with the prepared Co@NCNTs-MC as the support,which not only significantly improved the dispersion of Pt nanoparticles,but also enhanced the electron and mass transfer.The mass activity of methanol electrooxidation in Pt/Co@NCNTs-MC800-4was 700.3 m A mg_Pt^-1,which was about 4.5 times higher than that of 20%Pt/C.（2）The ZIF-8@ZIF-67 precursor was synthesized by the combination of ZIF-67 and ZIF-8,which are rich in nitrogen and carbon.The hollow porous carbon material of nitrogen-doped carbon nanotubes was synthesized at the appropriate temperature after high temperature calcination.The carbon nanotubes have good internal channels and fractional porous structure,and the hollow structure can further increase the specific surface area,so that the Pt based composite catalyst prepared has good electrochemical activity and stability.The mass activity of methanol oxidation in Pt/NCNTHPC800 samples can reach 416.2 m A mg_Pt^-1,which is about 2.5 times that of Pt/C.（3）A polypyrrole with high conductivity was prepared by electrochemical oxidation polymerization on the basis of ZIF-67.The optimum electrodeposition time was selected to make the ZIF-67 grow on the polypyrrole network and calcined at high temperature.The existence of polypyrrole network can inhibit the agglomeration of ZIF-67 at high temperature and keep the structure of ZIF-67 intact.The Pt based composite catalyst was synthesized using nitrogen-doped porous carbon as the support.The electrochemical test showed that the mass activity of methanol oxidation reaction of Pt/NPC-5 sample prepared using the catalyst as the support was 579.4 m A mg_Pt^-1,which was about 3.8 times that of commercial Pt/C.